What Does Metro Safety Monitoring Mainly Monitor?

Metro safety monitoring usually does not monitor a single structure; it builds a monitoring system around stations, running tunnels, tracks, subgrade and surrounding buildings, focusing on:

▪ Settlement, tilt and horizontal displacement of station main structures;

▪ Convergence, settlement, dislocation and local deformation of running tunnels;

▪ Vertical displacement and differential settlement of track structures;

▪ Displacement of foundation pit support structures, retaining walls and slopes;

▪ Settlement of the ground surface, surrounding buildings and underground pipelines;

▪ The impact of adjacent construction on existing metro structures.

GB 50911-2013 Code for Monitoring of Urban Rail Transit Engineering systematically specifies monitoring objects such as support structures, surrounding buildings, underground pipelines and existing rail transit structures. Actual projects should also determine monitoring items, measuring point layout, frequency and alarm values in combination with current mandatory engineering construction standards, local standards and special monitoring schemes.

Why Metro Safety Cannot Rely Only on Manual Inspection?

Manual inspection can find defects that have already appeared, such as cracks, leakage, spalling and obvious dislocation, but structural changes in metro tunnels tend to accumulate slowly.

For example, a single measurement showing small displacement at one point does not directly prove the structure has no risk. It also needs to be combined with:

▪ Whether displacement keeps growing;

▪ Whether the rate of change per unit time is accelerating;

▪ Whether differential deformation appears between adjacent measuring points;

▪ Whether changes synchronize with rainfall, precipitation, excavation or ground construction;

▪ Whether the structure can return to its original stable range after change.

Therefore, what metro safety monitoring really needs to answer is not how much it has moved now, but whether the structure is developing toward an abnormal state.

The Measures for Tiered Risk Management and Hazard Investigation of Urban Rail Transit Operation Safety issued by the Ministry of Transport in 2024 require operators to conduct comprehensive risk identification on their lines annually; when the operating environment changes significantly, dangerous events occur, or new equipment and technologies are introduced, special identification should also be carried out. For major risks, monitoring schemes and special emergency measures should be prepared.

This means monitoring data needs to enter risk identification, hazard investigation, warning notification and response decisions, rather than stopping at the data collection stage.

Which Data Matters Most in Metro Structural Monitoring?

1. Cumulative displacement

Cumulative displacement reflects how much the structure has changed relative to its initial state, suitable for judging long-term settlement, structural offset and differential deformation.

2. Change rate

The displacement has not reached the alarm value, but if the change speed suddenly accelerates, it may also mean external construction, groundwater or the structural load state has changed.

Therefore, alarms should not be set only as a cumulative value; the rate of change, continuous over-limit duration and correlations between measuring points should also be considered.

3. Adjacent Measuring Point Differences

Metro structures are usually continuous. Compared with all measuring points moving synchronously as a whole, obvious differences at local points deserve more attention, as they may correspond to local settlement, dislocation at joints or uneven loading.

4. Long-term trend

Temperature, train operation and environmental disturbance may cause short-term fluctuations. Only long-term data accumulation can distinguish normal fluctuations, periodic changes and persistent anomalies.

What Capabilities Should an Automated Metro Monitoring System Have?

A monitoring system oriented to long-term operation should usually focus on the following capabilities:

▪ Continuous acquisition: monitoring data is acquired automatically according to risk level and project requirements, reducing information loss caused by overly long measurement intervals.

▪ Multi-point coordination: grasp the changes of multiple measuring points simultaneously to judge whether an anomaly is local or global.

▪ Stable reference: when the device is affected by vibration, construction collision or environmental change, it should be able to identify reference changes and avoid misjudging device movement as structural displacement.

▪ Environmental adaptation: metro sites may have dust, humidity, lighting changes, equipment vibration and limited communication conditions; the system needs to adapt to long-term deployment environments.

▪ Tiered warning: set different warning levels according to cumulative displacement, change rate, continuous over-limit duration and measuring point correlations.

▪ Data retention: save raw data, trend curves, alarm records and response results, providing the basis for subsequent review, evaluation and maintenance decisions.

The Ministry of Transport's operational safety management measures clearly state that hazard treatment should form a closed loop of investigation, evaluation and rectification; when the situation is especially urgent, measures such as stopping operations, disabling facilities and equipment, blocking lines or closing stations may be taken as appropriate.

Therefore, the value of a monitoring system is ultimately reflected in whether it can provide timely, verifiable data as the basis for response measures.

Which Metro Scenarios Suit Vision-Based Displacement Monitoring?

Vision-based displacement monitoring usually places targets on the measured structure, with fixed measuring equipment continuously recognizing target position changes to compute structural displacement.

In metro safety monitoring, it can be applied to:

▪ Settlement and horizontal displacement monitoring of station main structures;

▪ Deformation monitoring of key cross-sections in running tunnels;

▪ Displacement monitoring of trackside structures and equipment foundations;

▪ Monitoring of the impact of adjacent foundation pit construction on metro structures;

Multiple measuring points, long distances, or areas inconvenient for manual access;

▪ Continuous monitoring for both temporary construction stages and long-term operation.

The advantage of vision monitoring is not simply filming the site, but converting position changes in images into continuous displacement data while retaining traceable image and trend records.

How Does Haytham Carry Out Metro Safety Monitoring?

Haytham online visual trackerUsing target recognition and vision measurement, it can perform non-contact displacement monitoring of multiple structural measuring points per project needs and upload data to the monitoring platform.

For metro site issues such as power access, communication, dense measuring points and long-term operation, the solution can be configured with:

▪ Automatic identification and numbering of multiple measuring points;

▪ Synchronized acquisition with multiple measuring heads;

▪ Long-distance flexible networking;

▪ Reference change identification and recalibration;

▪ Displacement trend analysis and tiered alarms;

▪ Cloud viewing, report export and interface integration;

▪ Power recovery and equipment operating status monitoring.

In Haytham's related project practice,Jinji Road Station of Hangzhou Metro Line 5 adopts a long-term online monitoring scheme; the Dan Shan Station project of Qingdao Metro Line 15 configured independent power supply and equipment self-monitoring for site conditions; the Xiangmei Station project of Shenzhen Metro adopted a single-device multi-point approach to improve measuring point coverage efficiency.

These applications show that metro safety monitoring schemes cannot simply copy an equipment list; they must be designed according to monitoring distance, number of points, on-site reference, power and communication conditions and risk level.

What Is the Core of Metro Safety Monitoring?

The core of metro safety monitoring is not how many devices are installed, but whether a complete data closed loop can be formed:

Detect changes → judge trends → identify anomalies → trigger warnings → on-site review → take measures → continuous review.

Only when monitoring data can be combined with inspection, construction conditions, environmental information and emergency response can metro safety management move from discovering defects after the fact to continuously tracking the development of anomalies.